The plastic fuel containers used in the automobile industry often include injection-molded plastic pipe nipples, which, for example, can be used for connecting an exhaust hose at a feeder pipe or for connecting a fuel hose to a fuel tank. These pipe nipples are connected to an opening in the feeder pipe or tank by a simple rotary weld.
Conventional tanks and their associated nipples consist of compatible plastics, such as un-reinforced high-density-polyethylene (HDPE). These plastic materials are selected primarily to provide a more dense, particularly diffusion dense, welding connection, for reusability, and for environmental compatibility. In addition, the plastics selected for use in automobile fuel tank applications should have a certain flexibility, so the tank can withstand a minimum load which may be applied in the event of an accident.
Conventional materials utilized in automobile fuel tank applications, especially un-reinforced HDPE, tend to soften or melt, or "creep", when subjected to higher local pressure loads, even at room temperature. If a flexible fluid-conduit, such as an elastomer-hose or a flexible plastic pipe, is connected with a plug-in or clamp-coupling which exerts high pressure locally on the pipe-nipple, even over a sealing O-ring, there is the danger that the connection between the pipe-coupling and the pipe-nipple will leak in time as a result of the pipe-nipple material's tendency to creep.
German application DE 3621948 A1 proposes to prevent creep in a thermoplastic pipe nipple on a plastic fuel tank by press-fitting a metal stiffening sleeve over the outside of the nipple. Attachment of a metal stiffener increases resistance to creep when high local pressure loads are applied, but does not provide a sufficiently permanent connection which will withstand the extreme vibration and temperature variations encountered in automotive applications.